Molecular Weight Cut-off Research Articles

Stereochemistry as a Parameter to Tune the Molecular Weight Cutoff in Solvent-Resistant Nanofiltration Membranes

Stereochemistry as a Parameter to Tune the Molecular Weight Cutoff in Solvent-Resistant Nanofiltration Membranes

Recovering rhamnogalacturonan-I pectin from sugar beet pulp using a sequential ultrasound and microwave-assisted extraction: Study on extraction optimization and membrane purification

This research focuses on the integrated recovery of rhamnogalacturonan-I (RG-I) pectin from sugar beet pulp (SBP). First, the extraction of RG-I pectin through sequential ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) was assessed. Optimization using a response surface methodology identified the optimal conditions as initial pH 4, 10 min of UAE, and 157 °C for MAE, achieving a 66.0 % recovery of pectooligosaccharides (POS). Additionally, purification through continuous diafiltration and concentration via ultrafiltration of the POS using membranes with different molecular weight cut-offs (MWCO) was explored. In contrast to previous research using discontinuous diafiltration, the use of continuous diafiltration allowed a decrease in the extract viscosity and obtained higher yields using a higher MWCO membrane. The refined RG-I pectin solids exhibited a high global yield (39–40 g pectin/100 g SBP), and high-methoxyl characteristics, as well as purity levels (70–80 %) similar to commercial prebiotics.

Removal of a cyanotoxins mixture by loose nanofiltration membranes applied in drinking water production

Cyanobacterial toxins may threaten human health if their levels in drinking water exceed certain thresholds. Therefore, it is important for water works that use raw water sources prone to cyanobacterial blooms to have efficient barriers against such toxins. Nanofiltration (NF) is one potential barrier. The efficacy and mechanism of removing four cyanotoxins, namely microcystins (MCs), cylindrospermopsin (CYN), saxitoxins (STXs), and anatoxin (ATX), were studied at bench-scale using NF membranes commonly applied in Norwegian drinking water facilities. The average removal of the different cyanotoxins under the tested operating conditions ranged from 15 % to 96 %. The membrane with the lowest molecular weight cut-off (MWCO) of 0.3 kDa made of polyamide (PA) was deemed the most suitable for the removal of all studied cyanotoxins. A gradual improvement of rejection observed with the 2 kDa cellulose acetate (CA) membrane was linked to the formation of fouling on the membrane surface. Sulfonated polyethersulfone (SPES) membranes with MWCO of 1 and 3 kDa could not efficiently and consistently remove cyanotoxins, except for MCs. The rejection of MCs over time was over 80 % by the SPES membranes during two days of filtration. The influence of pressure and pH as relevant operating parameters was evaluated. However, the analysis of the cyanotoxin concentrations in the permeate indicated that the investigated NF membranes alone would generally not be able to meet the WHO guidelines for drinking water during a severe cyanobacterial bloom. Thus, incorporating other water treatment technologies should be considered to effectively remove cyanotoxins.

Nanofiltration membrane performance of layer-by-layer membranes with different polyelectrolyte concentrations

Nanofiltration membranes produced with polyelectrolytes via the layer-by-layer technique are frequently researched, but misunderstood parameter is the polyelectrolyte concentration. Higher polyelectrolyte (PE) concentrations are known to produce thicker PE layers, but its effect on the membrane performance has only been studied in a limited fashion, leading to premature conclusions. In this work, two well-known strong polyelectrolytes, PDADMAC and PSS were used to prepare membranes using coating solutions with polyelectrolyte concentrations of 0.01, 0.1, 1.0, 2.5 and 5.0 wt% and two different salt concentrations in the coating solution of 0.05 and 1 M, as higher salt concentrations lead to thicker PE layers. The membrane performance of the prepared membranes is researched in terms of pure water permeability (PWP), molecular weight cut-off (MWCO) and the retention of different salts. In the first bilayer, membranes coated with a 0.05 M salt solution showed lower PWPs and MWCOs and higher salt retentions by increasing the PE concentration. After a certain number of coated bilayers, the MWCO and salt retentions reach a plateau for all PE concentrations; but the plateau value was obtained earlier by coating with a higher PE concentration. The membranes coated with the 1 M salt concentration had lower or comparable retention rates, except for MgCl2, than those coated with 0.05 M salt. The higher salt concentration resulted in more abundant PDADMAC in the membrane, which promotes the MgCl2 retentions for all bilayers. In conclusion, we found that the polyelectrolyte concentration significantly alters the membrane performance, but after coating 7 bilayers, the same size exclusion plateaus are reached.

Precise and ultra-wide molecular sieving capability with size-dependent COF layers for fast organic solvent nanofiltration

Four covalent organic framework (COF) layers with different alkyl side chains are used to create thin film composite (TFC) membranes via the improved unidirectional diffusion synthetic (UDS) technique. The synthesized membranes consist of polyacrylonitrile (PAN) substrates and TAPB-TPOCx COF (x = 1, 4, 6, and 8) layers, whose pore size and pore environment are tuned by direct integration of variable-length of TPOCx monomers. For organic solvent nanofiltration (OSN), we apply these COF membranes with variable thickness and pore size to test for the sieving ability of various organic pollutant surrogates. With the COF layers' bi-variable thickness and substituent length, the range cut-off molecular weight (330–970 g mol−1) for TAPB-TPOCx COF membranes involves the vast majority of OSN molecular sieving ranges. The COF membranes demonstrate precise molecular sieving capability with higher permeance of polar and nonpolar organic solvents than the state-of-the-art polymeric membranes.

Enhancement of water permeability in SiO2-ZrO2 nanofiltration membranes via adding organic solutes into the SiO2-ZrO2 sols

SiO2-ZrO2 nanofiltration membranes were prepared by adding glucose into SiO2-ZrO2 sols, followed by coating on cylindrical alumina porous support and firing at 550 °C. The average pore sizes of the SiO2-ZrO2 membranes by adding glucose in the SiO2-ZrO2 sols were larger than without adding glucose in sols. Water permeabilities of SiO2-ZrO2 membranes, prepared from 1.0 wt% SiO2-ZrO2 sols with and without the addition of 0.5 wt% glucose, were 4.2 × 10−12 m3/ (m2 s Pa) and 2.0 × 10−12 m3/ (m2 s Pa), respectively, while both of SiO2-ZrO2 membranes with and without addition of glucose showed approximately the same molecular weight cut-off (MWCO) of 300 g/mol.After membrane treatment in water at 90 °C, the water permeability of 1 wt% SiO2-ZrO2 membranes increased dramatically, while the MWCO of membranes remained the same as that before the treatment. The water permeability of membranes with and without addition of 0.5 wt% glucose increased from 4.2 × 10−12 to 9.1 × 10−12 m3/ (m2 s Pa) for MWCO of 320 g/mol and from 2.0 × 10−12 to 4.9 × 10−12 m3/ (m2 s Pa) for MWCO of 300 g/mol, respectively. An increase in the water permeability of SiO2-ZrO2 membranes after treatment in water at 90 °C can be explained by increasing in the hydrophilic surface and inner membrane pore and the dissolution of silica into hot water. SiO2-ZrO2 membranes with doping glucose achieved enhancement in the water permeability and hydrothermal stability.

Fabrication of phenolic resin membrane with polyvinyl alcohol fiber skeleton by electrospinning for organic solvent nanofiltration

As an emerging separation technology, organic solvent nanofiltration (OSN) has shown great potential in the chemical, food, and pharmaceutical industries. Considering the excellent solvent resistance of phenolic resin (PR), it has great potential to be employed for the fabrication of OSN membrane. However, the extremely low permeance due to the highly cross-linked network and limited fabrication strategies still hold back the further application of PR. Herein, we develop a novel method to fabricate PR membrane with polyvinyl alcohol (PVA) fiber skeleton for OSN. This is accomplished through the electrospinning of PVA-resol solution, followed by heating to initiate the cross-linking of resol to form PR. After the further reaction with glutaraldehyde (GA), the PR OSN membrane is finally acquired. Benefiting from the homogeneous mixing of PVA with resol in the electrospinning solution, the formed PVA fibers are uniformly embedded in the PR matrix. The space between PVA fiber skeleton with PR matrix could provide additional channels for the transportation of solvent molecules. Compared with those membranes fabricated by traditional casting methods, the permeance of PR/PVA/GA reported here is significantly improved. The molecular weight cut-off (MWCO) of PR/PVA/GA is about 803 Da based on the rejection curve. Meanwhile, the permeance of acetonitrile about 1.3 Lm-2h-1bar−1 is the highest among the studied solvents, while the values are very low for nonpolar solvents, such as hexane and toluene. Additionally, the obtained membrane exhibits excellent anti-compaction ability and long-term stability. As an alternative to phase inversion and interfacial polymerization, the strategy reported here may provide a new way for the assembly of polymers into nanofiltration membranes for diverse separation applications.

Effect of silver nanoparticles on the morphological, antibacterial activity and performance of graphene oxide-embedded polyvinylidene fluoride membrane

In this work, a different ratio of silver nanoparticles (Ag NPs) was used as a nanofiller on graphene oxide (GO)-embedded polyvinylidene fluoride (PVDF) membranes fabrication through a non-solvent induced phase separation method. The morphology of fabricated membranes was investigated using FTIR, XRD, and SEM-EDX techniques. The fabricated membranes were tested for Bovine Serum Albumin (BSA) rejection and Molecular Weight Cut Off (MWCO) with various initial concentrations of 100 – 400 ppm and 6 – 145 kDa, respectively using a crossflow method, as well as antibacterial activity against four strains bacteria via total plate counting and Kirby-Bauer method. The incorporation of hydrophilic GO and Ag NPs obviously alters membrane morphology, enhances membrane’s porosity and hydrophilicity. Moreover, it improves membrane crystallinity (> 70%) as indicated by the higher XRD peaks intensity. Based on the crossflow measurements, the membrane fabricated with GO and Ag ratio of 1: 3 (PVDF/GO/AgNPs – 3) demonstrated the highest BSA flux of 83.81 L/m2 h, which was third-fold higher than that of PVDF membrane as well as high BSA rejection (> 94%) and MWCO of ∼3 kDa. According to the observation, PVDF/GO/AgNPs – 3 also possessed a high bacteria killing ratio of > 94% and a large inhibition zone of ≥ 1.5 mm toward all bacteria strains. These results inferred that PVDF/GO/Ag membrane has great potential as antibiofouling membranes.

Carbon nanotubes regulated polyamide membrane by intercalation to improve the organic solvent nanofiltration performance

Carbon nanotubes (CNT) are considered as promising materials for enhancing thin-film composite (TFC) membranes by introducing an intermediate layer. However, the specific function of the CNT intermediate layer in the formation of the selective polyamide (PA) layer using interfacial polymerization (IP) remains unclear. Consequently, in this study, a network of CNT was applied as a coating on a polyketone (PK) substrate to control its surface characteristics and act as an intermediate layer for PA formation. By adjusting the amount of CNT, the PK surface became less hydrophilic and had smaller surface pores. The CNT intermediate layer facilitated PA formation by expediting the release of IP monomers, reducing the interaction between PK and the monomers. Nevertheless, excessive CNT loading could lead to the retreat of large leaf-like structures, which are essential for achieving high performance in organic solvent nanofiltration (OSN). OSN tests revealed that the optimal TFC-0.5 membrane displayed a methanol permeance of 5.34 L m−2 h−1/bar with an extremely low molecular weight cut-off (MWCO) of 170–180 g/mol. This result was attributed to the reduced PA intrusion, enlarged PA filtration area, and the gutter layer effect brought about by the CNT intermediate layer.

Investigating bromide incorporation factor (BIF) and model development for predicting THMs in drinking water using machine learning

Many disinfection byproducts (DBPs) in drinking water can pose cancer risks to humans while several DBPs including trihalomethanes are typically regulated. Although trihalomethanes are regulated, brominated fractions (bromodichloromethane, dibromochloromethane and bromoform) are more toxic to humans than the chlorinated ones (chloroform). To date, >100 models have been reported to predict DBPs. However, models to predict individual trihalomethanes are very limited, indicating the needs of such models. Various factors including natural organic matter (NOM), bromide ions (Br−), disinfectants (e.g., chlorine dose), pH, temperature and reaction time affect the formation and distribution of trihalomethanes in drinking water. In this study, NOM was fractionated into four groups based on the molecular weight (MW) cutoff values and their respective contributions to dissolved organic carbon (DOC), trihalomethanes and bromide incorporation factors (BIF) were investigated. Models were developed for predicting chloroform, bromodichloromethane, dibromochloromethane, bromoform and trihalomethanes. Three machine learning techniques: Support Vector Regressor (SVR), Random Forest Regressor (RFR) and Artificial Neural Networks (ANN) were adopted for training and testing the models. The normalized BIFs were in the ranges of 0.08–0.16 and 0.07–0.15 per mg/L of DOC for pH 6.0 and 8.5 respectively. The BIFs were higher for lower pH and MW values while increase of bromide to chlorine ratios increased BIFs. The models showed excellent predictive performances in training (R2 = 0.889–0.998) and testing (R2 = 0.870–0.988) datasets. The SVR and RFR models showed the best performances with lower RMSE and MAE in most cases. These models can be used to better control different trihalomethanes in drinking water to maintain regulatory compliance, and to minimize the risks to humans.

Stepwise UV crosslinking in solvent: A novel method to enhance the solvent resistance of poly(aryl ether ketone) membranes

In this contribution, the viability of using UV to give separation membranes a high crosslinking degree and broad-spectrum solvent resistance was investigated. A series of poly(aryl ether ketone) polymers suitable for UV crosslinking were first designed. And a unique photocrosslinking method, stepwise UV crosslinking in solvent, was developed by understanding photochemical reactions and molecular dynamics. This method does not require the introduction of additional photoinitiators and crosslinking agents, and the membrane preparation is a green and efficient process with a theoretical 100% atomic utilization rate. Combining this method with the special polymer structure design, a solvent-resistant nanofiltration membrane that can withstand strong polar aprotic solvents can be obtained. The molecular weight cut off of the membrane in N,N-dimethylformamide was 300 g/mol, and the permeance was 1.154 L m−2 h−1 bar−1. This separation effect even exceeded that of most composite membranes. After testing, the membranes prepared using this method had the ability to maintain functional stability at 80 °C in N,N-dimethylformamide for one month. The excellence of membrane performance and the flexibility of regulatory methods both reveal the enormous potential of this method.

UF fractionation of fish protein hydrolysate

A commercial fish protein hydrolysate was fractionated using polymeric spiral wound ultrafiltration (UF) membranes. As protein hydrolysates are electrolytes, the effects of pH and ionic strength were investigated. Three different polyethersulfones (PES) membranes with different nominal molecular weight cut-offs (10, 5, and 3 kDa) and a polyamide-thin film composite (PA) membrane with a nominal molecular weight cut-off of 3 kDa were used. The membrane flux and retention profile, and the selectivity for <4 kDa peptides were analyzed and discussed. The PES membranes were suitable for fractionation of the hydrolysate, while the PA membrane showed high retention for all components because of the adsorption of solutes to the membrane surface. The results showed that with charged solutes, the nominal molecular weight cut-off as supplied by manufacturers was not the decisive parameter for choosing a membrane. The permeate flux at pH 8 was higher than that at pH 5 for all PES membranes. The presence of salt in the hydrolysate significantly improved the flux and selectivity. The overall retention mainly was dependent on the retention of small peptides (<4 kDa). The mass transfer mechanism of charged peptides within the concentration polarization during UF separation was simplified and presented regarding size and charge exclusions.

Intramodule pressure profiles and protein accumulation during tangential flow filtration.

Tangential flow filtration (TFF) through a 30 kDa nominal molecular weight cut-off (MWCO) ultrafiltration membrane is widely employed to concentrate purified monoclonal antibodies (mAbs) to levels required for their formulation into injectable biologics. While TFF has been used to remove casein from milk for cheese production for over 35 years, and in pharmaceutical manufacture of biotherapeutic proteins for 20 years, the rapid decline in filtration rate (i.e., flux) at high protein concentrations is a limitation that still needs to be addressed. This is particularly important for mAbs, many of which are 140-160 kDa immunoglobulin G (IgG) type proteins recovered at concentrations of 200 mg/mL or higher. This work reports the direct measurement of local transmembrane pressure drops and off-line confocal imaging of protein accumulation in stagnant regions on the surface of a 30 kDa regenerated cellulose membrane in a flat-sheet configuration widely used in manufacture of biotherapeutic proteins. These first-of-a-kind measurements using 150 kDa bovine IgG show that while axial pressure decreases by 58 psi across a process membrane cassette, the decrease in transmembrane pressure drop is constant at about 1.2 psi/cm along the 20.7 cm length of the membrane. Confocal laser scanning microscopy of the membrane surface at the completion of runs where retentate protein concentration exceeds 200 mg/mL, shows a 50 μm thick protein layer is uniformly deposited. The localized measurements made possible by the modified membrane system confirm the role of protein deposition on limiting ultrafiltration rate and indicate possible targets for improving membrane performance.

Enrichment of lycopene in watermelon juice by ultrafiltration: technical assessment and fouling analysis

SummaryWatermelon juice is proven to be a potential source of lycopene, but its exploitation and consumption are currently constrained. The research focused on lycopene enrichment in watermelon juice by ultrafiltration (UF) with 1000 Da of molecular weight cut‐off (MWCO). The selectivity of UF membrane for the constituents in watermelon juice was investigated from 2 to 8 bar by dead‐end mode combined with stirring. The 1000 Da UF membrane showed a high potential to recover and separate lycopene from other components. However, membrane deposition and capillary occlusion could occur, affecting the overall efficiency of the enrichment process. To better understand kinetics, phenomena and efficiency, the study was evaluated in cross‐flow mode with full recirculation of retentate. The enrichment efficiency was found to increase the concentration and purity of lycopene by several times. The concentration polarisation was used to describe permeate flux decline, while the Hermia model was developed to explain fouling mechanisms. The utilised models were highly compatible; additionally, pore blocking was thought to be the main mechanism of fouling in lycopene enrichment by 1000 Da UF. The built mathematical model was in good agreement with the experimental observations of permeate flux, and lycopene, TS and ash concentrations. The 1000 Da UF of watermelon juice is a feasible approach for lycopene enrichment.

Tailoring the performance of composite PEI nanofiltration membranes via incorporating activated cyclodextrins

Cyclodextrins (CDs) with unique cavity structures have been used as materials for nanofiltration membrane fabrications. In the present work, the activated CD (O-CD), oxidated by NaIO4, and polyethyleneimine (PEI) were co-deposited on a hydrolyzed polyacrylonitrile support, post-treated by glycerol protection and heating treatment, to prepare nanofiltration membranes with low molecular weight cut-off (MWCO). As the cavities in CD present and the aldehyde groups introduced after oxidation, the O-CDs were expected to crosslink the PEI layer and provide extra permeating channels. The filtration experiments showed that the incorporation of O-CDs improved the permeances of the O-CD-PEI/HPAN nanofiltration membranes. The performance can be tailored by the control of the loading or the oxidation degree of the O-CD. At optimal conditions, the permeance increment was nearly double (from 9.2 to 21.1 Lm-2·h−1·bar−1). While the selectivity was without significant sacrifice, the rejection of PEG 200 remained around 90%. Meanwhile, the membrane stability was demonstrated by pro-longed filtratiing a PEG 200 aqueous solution. The constant permeance and rejection confirmed the O-CD-PEI/HPAN membranes were stable. The incorporation of activated CD in PEI offers a facile strategy to promote the permeance of PEI-based membranes.

Solution-processable poly(ether-ether-ketone) membranes for organic solvent nanofiltration: from dye separation to pharmaceutical purification

Through polymer engineering, the membrane properties can be considerably changed and its performance can be improved. Organic solvent nanofiltration (OSN) membranes require polymers with good solution processability to facilitate membrane preparation. However, the resultant membranes should have excellent solvent resistance. Poly(ether-ether-ketone) (PEEK) is a potential polymer for OSN applications because of its high thermal stability and excellent solvent resistance. However, commercial PEEK has limited solution processability, and its fabrication requires a harsh acidic environment. Herein, two customized PEEKs were synthesized by incorporating methyl (–CH3) and sulfonyl (SO2) groups into the polymer backbone. The membranes were prepared by phase inversion using N-methyl-2-pyrrolidone (NMP) and TamiSolve as a green alternative. The effects of the polymer structure, green solvent, and crosslinking on the membrane morphology, chemical and mechanical stability, as well as separation performance have been examined. The molecular interaction between organic solvents and PEEKs were investigated through molecular dynamic simulations and density functional theory. The molecular weight cutoff (MWCO) values of the membranes were 540–768 g mol−1, with a high corresponding permeance of 8.2–20 L m−2 h−1 bar−1 in acetone. The long-term stability of membranes was successfully demonstrated over two weeks through a continuous crossflow filtration using acetone under a pressure of 30 bar. The membranes demonstrated excellent active pharmaceutical ingredient purification through the removal a 2-methoxyethoxymethyl chloride (125 g mol−1) carcinogenic impurity from roxithromycin (837 g mol−1).

Linear solvation energy relationships for adsorption of aromatic organic compounds by microplastics

This study develops predictive models for adsorption of organic compounds (OC) by microplastics using linear solvation energy relationship (LSER). The adsorption mechanism of aromatic OCs by microplastics was investigated by delineating the effect of molecular weight of the OCs, polymer type of MPs, and background water chemistry. The benchmark model for adsorption of OCs (n = 28) by polyethylene yielded an R2 = 0.85 (n = 28), RMSE = 0.38, Q2LOO = 0.73. Further narrowing the dataset down by decreasing the molecular weight cutoff to OCs < 192 g/mol improved the model to R2 = 0.98 (n = 13). Validation techniques tested the predictive strength of the benchmark model, which included new experimental adsorption data and performing leave-one-out cross validation. Among LSER model descriptors, the molecular volume was the most predominant descriptor in all scenarios, suggesting the importance of non-specific interactions and OC hydrophobicity. The results demonstrated that LSER is a promising approach for predicting the adsorption of aromatic OCs by MPs.

Reuse of end—of—life membranes through accelerated polyamide degradation

End—of—life (EoL) thin—film composite (TFC) reverse osmosis membranes were converted into ultrafiltration—like (UF) membranes in an accelerated degradation process of the polyamide (PA) using an oxidant (NaOCl) in the presence of either MgCl2 or CaCl2. The PA degradation was evaluated by measuring pure water permeability (PWP), MgSO4 passage and molecular weight cut—off; the more PWP increased, and the less MgSO4 was retained after treatment, the more the PA was degraded. By adding 10 mM of metal ions, PWP increased 2.1 (MgCl2) and 3.1 (CaCl2) times compared to the increase achieved with hypochlorite alone (2560 ppm∙h of free chlorine). Changes in the membranes after treatment were analyzed by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE—SEM), and by measuring their surface charge and contact angle. FTIR and FE—SEM confirmed the PA layer degradation. FE—SEM micrographs showed that full removal of the PA layer can be achieved by using an oxidation dose of 12,700 ppm∙h when Ca2+ is used but doses as high as 300,000 ppm*h are needed without catalyst. The results proved that by controlling the oxidation process it was possible to control the cut—off (MWCO) value of the membrane from 16,100 g∙mol—1 to 27,100 g∙mol—1. Before treatment, EoL membranes showed a MWCO of approximately 1200 g∙mol—1, meaning that molecules with that size could be retained in a 90%. In summary, the presented method enables reducing waste by the conversion EoL membranes into tailored UF—like membranes and by decreasing the amount of oxidant used in the conversion process.

Polyamide thin film nanocomposite with in-situ co-constructed COFs for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is a novel membrane technology, it has great potential for organic solvent separation and purification due to its advantages of low energy consumption and mild operating conditions. High-performance OSN membranes are essential for OSN technology. Herein, we adopted a straightforward one-step in-situ co-polymerization procedure for the fabrication of a thin film nanocomposite (TFN) OSN membrane having a COFs-polyamide selective layer via doping the COFs reaction monomers, p-phenylenediamine (Pa) and 1,3,5-triformylphloroglucinol (Tp), into the aqueous m-phenylenediamine (MPD) solution and organic trimesoyl chloride (TMC) solution, respectively, during the interfacial polymerization (IP) process. With the ultra-low concentrations used in both MPD and COFs reactive monomers, the optimal TFN OSN membrane, TFN-100-75, achieves an ethanol permeance of 65.7 L m−2 h−1 MPa−1 and an Rhodamine B (RDB, 479 Da) rejection of 99.0%. Meanwhile, this OSN membrane has an ultra-smooth surface, corresponding to a roughness of only 2.9 ± 0.3 nm. Also, this membrane has larger porosity, average pore size, and surface pore density compared with the COFs-free thin-film composite (TFC) membrane. Besides, the TFN-100-75 membrane has a pure methanol and ethanol permeance of 184.3 and 105 L m−2 h−1 MPa−1, respectively, and a molecular weight cut-off (MWCO) of about 362 Da. The TFN-100-75 membrane achieved an rifampicin rejection of above 99% during the separation of rifampicin/ethanol solutions with different concentration as well as the continuous concentration experiment, demonstrating its potential in pharmaceutical separation and purification. During a long-time variable temperature immersion test in pure N,N-dimethylformamide (DMF) at 25 °C for 32 days and then at 80 °C for 24 days, the TFN-100-75 membrane demonstrates superior solvent resistance, where the RDB rejection decreased only by 2%, from 99.0% to 97.0%. The TFN OSN membrane fabricated by the simple process in this work shows better separation performance than most OSN membranes reported in literatures, and has bright prospects for industrial organic solvents treatment.

Effects of graphene oxide membrane thickness reduction on microstructure and crossflow separation performance in kraft black liquor dewatering

Reduced graphene oxide (rGO) membranes are emerging as viable candidates for energy-efficient fractionation of multicomponent biomass streams, such as kraft black liquor (BL). Increased fluxes in rGO membranes under crossflow conditions – while maintaining high solute rejections – are highly desirable for improving the economics of such processes. We have conducted a detailed experimental study of a series of rGO membranes with progressively lower thicknesses (from 130 nm to 40 nm). The influence of the membrane thickness and the membrane microstructure is analyzed in terms of its effects on water permeation flux, divalent salt rejection, and molecular weight cutoff (MWCO) measurements using dye molecules. A selected rGO membrane (70 nm) showing both high fluxes and rejections was scaled up to a 650 cm2 sheet and used for extended crossflow operation under real BL streams for more than 22 days. Techno-economic calculations reveal significant positive effects of membrane thickness reduction on the economics of BL dewatering.